The present invention relates to a roller bearing and, in particular, to a roller bearing including a plurality of rolling members each of which is formed in a substantially conical shape, a substantially cylindrical shape, or a similar shape.
In a roller bearing including a plurality of substantially cylindrical-shaped or substantially conical-shaped rolling members (which are hereinafter referred to as rollers), if there occurs an axis shift, that is, if the axes of outer and inner races intersect each other, then, in a contact portion between the race surface (so called as an outer racetrack) of the outer race and the rollers and/or a contact portion between the race surface (so called as an inner racetrack) of the inner race and the rollers, on one side of the position there the roller end portions are contacted with the race surfaces of the inner and/or outer races, there may occur locally an increase in the contact pressure (which is hereinafter referred to as edge stress), which raises a fear that the roller bearing may be damaged in the early stage.
Therefore, when mounting the roller bearing onto various devices, it is necessary to make the axes of the outer and inner races coincide with each other with high accuracy, but, in fact, there is a possibility that the axes of the outer and inner races can be shifted/deviated from each other if the rotary shaft of the roller bearing is flexed due to a large axial load.
In order to avoid the above problem, conventionally, there is used a roller bearing in which a crowning operation such as a full crowning operation or a partial crowning operation is performed on the surfaces of the inner and outer races and/or the peripheral surfaces (which are hereinafter referred to as rolling surfaces) of the respective rollers (that is, a conventional roller bearing).
Here, the crowning operation means an operation which works the whole or given areas of buses forming the surfaces of the inner and outer races or the whole or given areas of buses forming the rolling surfaces of the rollers into convex-shaped curved surfaces.
By the way, in the above-mentioned conventional roller bearing, in a large axis shift angle (in which the axes of the outer and inner races can be shifted/deviated from each other by a relatively large angle), in order to prevent the edge stress from occurring between the race surfaces and the rolling surfaces, the radius of curvature of the portion to be crowned must be set small.
However, if the radius of curvature of the portion to be crowned is set small, when the axis shift angle is small (in which the axes of the outer and inner races can be shifted/deviated from each other by a relatively small angle), or when no axis shift occurs, the surface pressures in the central portions of the contact portions between the respective race surfaces and rollers are inconveniently high when compared with a case in which no crowning operation is performed or a case in which the radius of curvature of the portion to be crowned is set large.
The present invention aims at eliminating the above drawbacks found in the conventional roller bearing. Accordingly, it is an object of the invention to provide a roller bearing which can prevent occurrence of an edge stress in a large axis shift angle produced between the outer and inner races, and also, even when the axis shift angle between the outer and inner races is small, can control an increase in the surface pressures in the central portions of the contact portions between the surfaces of the outer and inner races and the rolling surfaces of the rollers.
The above-mentioned object can be achieved by a roller bearing according to the present invention comprising an outer race including an outer race surface which is formed on the inner peripheral surface thereof which is defined by rotating an outer race surface defining bus about an axis thereof, an inner race including an inner race surface which is formed on the outer peripheral surface thereof and is defined by rotating an inner race surface defining bus about the axis, and a plurality of rolling members respectively interposed between the outer and inner race surfaces in which an outer peripheral surface of each of the rolling members is defined by rotating a rolling surface defining bus. At least one of the outer race surface defining bus, the inner race surface defining bus and the rolling surface defining bus comprises a first radius of curvature. Each of the others of the outer race surface defining bus, the inner race surface defining bus and the rolling surface defining bus comprises,
a first bus having a second radius of curvature which is different from the first radius of curvature and substantially disposed at a center in an axial direction of the roller bearing and
second buses disposed both sides of the first bus, each of the second buses having a third radius of curvature which is different from the first radius of curvature and is also different from the second radius of curvature.
In the above-mentioned construction according to the present invention, it is preferable that each of the outer race surface defining bus and the inner race surface defining bus has the first radius of curvature, and the rolling surface defining bus comprises the first bus and the second buses.
Further, in the above-mentioned construction according to the present invention, it is also preferable that each of the outer race surface defining bus and the inner race surface defining bus comprises the first bus and the second buses, and the rolling surface defining bus has the first radius of curvature.
Moreover, in the above-mentioned roller bearing, it is preferable that each of the outer race surface and the inner race surface is a concave shape, and also the first radius is larger than the second radius, and the second radius is larger than the third radius.
In addition, in the above-mentioned roller bearing, it is advantageous that each of the outer race surface and the inner race surface is a convex shape, and also the first radius is smaller than the second radius, and the second radius is smaller than the third radius.
Further in attaining the above object, according to one aspect of the invention, there is provided a roller bearing comprising an outer race including a concave-shaped race surface formed on the inner peripheral surface thereof, an inner race including a concave-shaped race surface formed on the outer peripheral surface thereof, and a plurality of substantially cylindrical-shaped rolling members respectively interposed between the concave-shaped race surfaces of the outer and inner races, the outer peripheral surface of each of the rolling members being formed by a convex-shaped bus, wherein each of central portions in one of the concave-shaped race surfaces of the outer and inner races and the outer peripheral surfaces of the rolling members is formed by a first bus having a given radius of curvature, and two end portions respectively adjoining the central portion are respectively formed by second buses each having a radius of curvature which causes the two end portions to be separate from the other of the concave-shaped race surfaces of the outer and inner races and the outer peripheral surfaces of the rolling members.
Also, according to another aspect of the invention, there is provided a roller bearing comprising an outer race including a convex-shaped race surface formed on the inner peripheral surface thereof, an inner race including a convex-shaped race surface formed on the outer peripheral surface thereof, and a plurality of substantially cylindrical-shaped rolling members respectively interposed between the convex-shaped race surfaces of the outer and inner races, the outer peripheral surface of each of the rolling members being formed by a concave-shaped bus, wherein each of central portions in one of the convex-shaped race surfaces of the outer and inner races and the outer peripheral surfaces of the rolling members is formed by a first bus having a given radius of curvature, and two end portions respectively adjoining the central portion are respectively formed by second buses each having a radius of curvature which causes the two end portions to be separate from the other of the convex-shaped race surfaces of the outer and inner races and the outer peripheral surfaces of the rolling members.
Here, in the roller bearing according to the invention, the concave-shaped race surfaces of the outer and inner races as well as the outer peripheral surfaces of the rolling members (or rollers) may be formed by the first and second buses which continue with each other and have different radii of curvature.
In more particular, to form the rolling surface of each roller using the first and second buses, the central portion of the rolling surface of the roller may be formed by the first convex-shaped bus which corresponds to the buses of the respective concave-shaped race surfaces and, at the same time, the two end portions of the rolling surface of the roller may be respectively formed by the second convex-shaped buses each having a radius of curvature smaller than that of the first bus.
On the other hand, to form each of the respective concave-shaped race surfaces of the outer and inner races, the central portion of each of the respective concave-shaped race surfaces may be formed by the first concave-shaped bus which corresponds to the bus of the rolling surface of the roller and, at the same time, the two end surface sides of each concave-shaped race surface may be respectively formed by the second concave-shaped buses each having a larger radius of curvature than the first bus.
In addition, in the above-mentioned roller bearing according to the present invention, it is advantageous that a center of curvature of the concave-shaped bus defined by the concave-shaped race surface of the outer race is positioned at a position further than the axis of the roller bearing. In this case, the edge load can be remarkably and effectively suppressed.
Further, in the above-mentioned roller bearing according to the present invention, it is advantageous that a center of curvature of the convex-shaped bus defined by the convex-shaped race surface of the inner race is positioned at a position further than the axis of the roller bearing. In this case, the edge load can be remarkably and effectively suppressed.
Also, in the above-mentioned roller bearing according to the present invention, the convex-shaped race surfaces of the outer and inner races as well as the outer peripheral surfaces of the rolling members (or rollers) may be formed by the first and second buses which continue with each other and have different radii of curvature.
In more particular, to form the rolling surface of each roller using the first and second buses, the central portion of the rolling surface of the roller may be formed by the first concave-shaped bus which corresponds to the buses of the respective convex-shaped race surfaces and, at the same time, the two end portions of the rolling surface of the roller may be respectively formed by the second concave-shaped buses each having a radius of curvature larger than that of the first bus.
On the other hand, to form each of the respective convex-shaped race surfaces of the outer and inner races, the central portion of each of the respective concave-shaped race surfaces may be formed by the first convex-shaped bus which corresponds to the bus of the rolling surface of the roller and, at the same time, the two end surface sides of each convex-shaped race surface may be respectively formed by the second convex-shaped buses each having a larger radius of curvature than the first bus.
In addition, in these cases, in order that the boundary line between the first and second buses cannot provide a ridge or a groove, the first and second buses may be so formed as to continue with each other smoothly, or a chamfering operation may be performed along the boundary line between the first and second buses.
By the way, the above-mentioned concave-shaped race surfaces, convex-shaped race surfaces, and rolling members are not limited to those which are formed by the first and second buses; but, they can also be formed by two or more kinds of buses.
In the conventional roller bearing, contact between the crowned race surfaces and the rolling surfaces of the rollers is carried out in the form of mutual contact between the convex-shaped buses by which the race surfaces and roller rolling surfaces are formed. On the other hand, in the above-mentioned structures according to the invention, the race surfaces formed by convex-shaped buses are to be contacted with the roller rolling surfaces formed by buses each having a corresponding shape, that is, the roller rolling surfaces formed by the concave-shaped buses. Thanks to this, even when the axis shift angle between the outer and inner races is small, or even when no axis shift is present between the outer and inner races, there is no fear that the contact surface pressure between the respective race surfaces and the rolling surfaces of the rollers can be increased up to a high pressure.
Also, in the present two roller bearings, since there are produced relatively large clearances respectively between the race surfaces and the rolling surfaces of the rollers, even if there occurs a relatively large axis shift between the outer and inner races, there is no possibility that an edge load or the like can be generated.
In addition, in the case where a bus configuration of each of the aforementioned rolling surface and race surfaces are formed by a plurality of buses having different radii of curvatures, it is possible to connect them more smoothly at its boundary portions, to thereby suppress an increase in the surface pressures between the respective race surfaces and the respective rolling members.
Therefore, in these roller bearings, when compared with the conventional roller bearing, a large axis shift angle to be produced between the outer and inner races can be coped with properly and also, even when the axis shift angle between the outer and inner races is small, an increase in the surface pressures between the respective race surfaces and the respective rolling members can be controlled, whereby the above-mentioned object of the invention can be achieved.
By the way, in these roller bearings, to control the rise in the surface pressure in the boundary between the first and second buses having different radii of curvature, there can be employed a structure in which the first and second buses have a common tangent in the boundary between them, or a structure in which there is formed a third bus in such a manner that it extends astride the first and second buses.